Dynamometer instrument



Oct.- 15, 1940. A..J,:Q so- I 2,218,376

DYNAMOMETER INSTRUMENT Filed .Oct. 25, 1958 Mayne/1.2:

Shield III "I u M I II II "1% 45 4 Inverw tor:

46 I Almon J. Corson,

His Attorney.

Patented Oct. 15. 1940 UNITED STATES nYnAMoMn'i'an INSTRUMENT Almon Corson, Swampscott, Mass, assignor to General Electric Company, a corporation of New York Appiigamn October is, loss, Serial n3. 236,891

Claims.

My invention relates to current responsive instruments and concerns particularly instruments and current responsive devices of the dynamometer type. i 5 It is an object of my invention to provide in an electrical instrument a long or wide-angle scale. Furthermore it is an object of my invention to provide such an instrument in which the scale is relatively uniform throughout its length. Another object of my invention is to provide a high torque current responsive device and to' provide a construction in which iron cores may 1 be used for the current conducting coils to increase the available magnetic flux..

Still another object of my invention is to pro-' vide a current responsive device which is suitable for either direct current or alternating current and in which electromagnets' are available for.

producing the magnetic flux.

m It is a further object of my invention to provide aninstrument which is suitable formeaSuring the product of electrical currents; particularly for measuring vector products, as in the case of alternating currents differing in phase :5 relationship. It is also an object'of my invention to provide a construction which may be used not onlyfor instruments of the product type such as wattmeters and reactive-component-of-power meters 30 but also for dynamometer type voltmeters and ammeters.

Still another object of. my invention is to construct an iron core type of dynamometer instru- 'ment in such a manner that the movable coil rea mains at a zero position and does not produce any torque when no current is flowing in the field coil thus obviating the necessity for auxiliary or torque compensating coils.

It'is also an object of my invention to provide an alternating current instrument which is substantially free from errors, including errors such as wave form errors, for example.

Other and further objects and advantages will become apparent as the description proceeds.

a In carrying out my invention in its preferred form I provide a field structure having an outer pole piece and an inner pole piece. which is very nearly surrounded by the outer pole piece and spaced to form an annular air. gap 250 in length 50 through which an eccentrically'mounted coil may rotate. The inner pole piece has an opening through the center through which passes one side of the coil together with the shaft supporting the coil. The core member including the in- I so ne'r pole piece is divided so as to have the general form of'a U. There are arms or branches, which extend from the outer pole piece to the ends of the U to complete the magnetic circuit of the. field. However, air gaps are interposed between the inner pole piece and the arms leading from 6 the outer pole piece in order to increase the reluctance in the-path of magnetic flux which tends to be produced by the movable coil. A stationary or field coil is wound around the neck or base portion of the outer pole piece. In the 10 .case of a wattmeter, for example, the field coil may be formedas a current coil and the mov able coil as. a potential coil of the instrument.

The invention may be understood more readily from the following detailed description when 15' considered in connection with the accompanying drawing and those features of the invention which are believed. to be novel and patentable will be pointed out in the claims'appended hereto. In the drawing Figure 1 is a front elevation partially in section with certain portions of the apparatus broken away for the sake of clarity showing the torque producing unit of a dynamometer type instrument constructed in accordance with my invention. Figure 2 is a side elevation of the arrangement of Figure 1 also shown partially in section with a portion of the apparatus broken away. .Figure 3 is a circuitdiagram illustrating the arrangement for obtaining power factor compensation of the instrument and show the phase angle effect of the losses in the iron core, and Figure 4 is -an illustration of another embodiment of my invention adapted to use in polyphase alternating current circuits.

for various types of dynamometer instruments such as alternating and direct current voltmeters and ammeters, for example, it is particularly use ful with. wattmeters and I shall describe the arrangement with particular reference to its use as a wattmeter. For this purpose it is usually most convenient to wind the movable coil ll with relatively fine wire connected in series with a suitable multiplier or resistance coil to serve as the potential coil of the wattmeter and to wind the field coil with a suitable number of turns of heavy wire to serve as the current coil of the wattmeter.

In order to obtain a wide angle of movement of the rotatable current conducting" coil II, the field iron of the instrument is arranged with an inner annular polepiece I4 which is very nearly surrounded. by an outer pole piece I5. One side of the coil II and the shaft I6 to which the said side of the coil II is secured-pass through the center of the annular pole piece I4: The outer pole piece I5 is integral with a field member H which, in the arrangement shown, may be generally in the shape of a c with the pole piece I5 constituting a projection extending inwardly from the mid portion of the C, the projection or pole piece I5 having a circular notch therein for the inner pole piece I4. The field iron is completed by a core for the movable coil II formed by the core unit l8, which is generally in the shape of a U with the yoke portion forming the annular inner pole piece l4 and with leg portions I9 and 20 spaced to leave an air gap between them.

The endportions 2I and 22 of the C-shaped field I! approach very closely to the sides of the ends I9 and 20 of the U-shaped core unit I8.

I Preferably the end portions ,of the field I1 and the core unit I8 do not come into immediate contact but leave, perceptible air gaps 23 and 24 for the purpose of reducing field saturation and overcoming wave form errors of the instrument. In the preferred arrangement which I have illustrated although air gaps 23 and 24 are relatively small and less than the air gap I2 within which the outer side of the movable coil II travels, the air gap I2 in turn is less in length than the air gap 25 between the leg portions I9 and 20 of the U-shaped core I8.

It will be understood, of ciseshapes of. the field and core members are immaterial and that any shape may be employed which would provide a flux conducting path from the outer pole piece I5 to the inner pole piece I4.

However, in order to avoid having the rotatable coil II subject to having force applied to it solely due to the action of current flowing through it,

I prefer to have the core l8 constructed in some form of the. nature of that shown where the portion' of the material connected to the pole piece I4 is divided so as to have the air gap 25 between said divided portions, and preferably the core I8 has a relatively symmetrical configuration at least in the portion thereof close m1 the inner annular pole piece I4. It will be seen that in the arrangement illustrated the entire field structure is relatively symmetrical, so that flux produced by the field coil I3 mounted on the neck 26 of the pole piece I5 divides substantially equally between the branches 2'! and 28 and between the leg portions I9 and 20 to the inner annular pole piece l4, where the two flux paths join, and the fin: passes across the gap I2, back to the outer pole piece I5. The annular pole piece I4 may be regarded as having a gap 25' in the annulus with the core portions I9 and 20 extending from either side of said gap 25. My invention, however, is not limited to this precise arrangement since the air gap I2 is relatively uniform course, that the preand causes the flux to distribute itself substan my invention is not limited to the use of iron for a the flux conducting portion of the apparatus butthat any suitable material having relatively high I be obtained.

The method of supporting the various parts of ,the apparatus will be seen more readily from Figure 2 showing an enclosing casing 29, partially broken away, in which the E-shaped-frame 30 is secured for supporting the parts of the instrument. It will be seen that the frame 30 includes a pair of relatively long, narrow, upwardly extending arms 3! and 32 and, in the ends of these arms, suitable bearings or jewels 33 and 34 are mounted, which have hard surfaced cup shaped depressions in which mechanical pivot points 35 and 36 formed at the ends of the shaft I6 are permitted to rotate. A relatively wide and spreading arm or bracket 3'! is provided at the intermediate portion of the frame 30 for supporting the field laminations I! by means of suitable bolts 38. The core laminations I8are likewise secur'edto thebracket 31 by means of suitable bolts 39.

A pointer 40, and if desired, a suitable damping vane, not shown, are secured to the shaft I6 and it will be understood that suitable means such as lead-in spirals, not shown, for connecting the potential terminals of i the instrument to the rotatable coil II and a biasing spring, not shown, are also provided. The scale, not shown, for cooperation with the pointer 40, it will be understood, is to be mounted within the front cover 4| of the casing 29 and may be secured to the arm 3|. v 1

My construction lends itself to convenient and expeditious assembly. The assembly may be carried out in the following manner. After the coil I I has been mounted 'upon the shaft I6 the shaft I6 may be inserted between the bearings 33 and 34 and secured by a suitable longitudinal adjustment of the bearings. By turning the coil II to a horizontal position core unit I8 may be slipped through the'coil II and over the shaft I6 whereupon the core unit I8 is bolted to the bracket 31 of the frame 30. After the field coil 26 has been slipped on tothe pole piece l5 and secured thereto, the field member I! maybe passed longitudinally of theshaft I6 past the arm 32 around the pole piece I4 and is also bolted to the bracket 31. It will be understood that other parts, not shown, such as the scale plate, etc., may be secured to the front bracket 3| of the frame 30 structure for "increasing the rigidity of the assemblyl I If the apparatus is to be used as a voltmeter or an ammeter, it will be understood that the coils II and I3 may be connected in series, whereas if it is to be used as a. wattmeter, the field coil I3 will be connected in series to the load directly or to a suitable transformer and the potential coil II will be connected between the lines of the circuit tested or between the' output" terminals of the potential transformer in series with a suitablemultiplier resistance. Assuming that the apparatus is used as a wattmeter it will core unit it is symmetrically constructed and the reactance of the current conducting coil II is substantially the same for any position there is substantially no tendency for the current flowing in the coil II to produce a torque when there is no current flowing in the field coil l3. However, there is a tendency for the current flowing through the coil II to cause a fiux to pass through the'stationary iron oi the apparatus, up one leg IQ of the U shaped core unit l8, down leg 20, through the branch 28, and down branch 21 to the end of the core unit l8, or vice versa. This fiux, however, serves no particular purpose as it is only the flux from the coil ll crossing the air gapl2 and reacting with the torque produced by the coil. l3 that produces torque. If the idle flux produced by the coil H, however, should be excessive it would tend to increase the inductance and decrease the power factor of the potential circuit and might also produce saturation effects which, in turn, may lead to wave form errors. To obviate thistendencythe air gaps 2'3 and 24 are provided between the end portions 2| and 22 of the field member l I and portions l9 and 20 of the coreunit It.

The use of iron cores in precision'instruments such as wattmeters may introduce some power factor errorsdue to the hysteretic angle of advance or the phase displacement, produced by the iron losses, between the actual current flowing in the coils and the component thereof serving as a magnetizing current. If it is desired to compensate for such errors a compensating condenser 44 may be provided as shown in Figure 3. In Figure 3 the inductance 45 represents the potential coil ll, resistance It represents the inherent resistance of the potential coil, the resistances 41 and 48 represent two-sections of series connected resistance spools or multipliers to limit the current to a suitable value, and the inductances 49 and 50 represent the unavoidable inductances of the resistance spools 4'! and 48. It will be seen that the compensating condenser ll is connected from a point on one side of the coil 45 to a point between sectionsof the currentlimiting resistances 41 and 48.

Although in discussing the use of my apparatus as a wattmeter, I have described an instrument which would serve as a single phase wattmeter, it will be understood that my invention is not limited to this precise arrangement and that by placing a number of units in line with the rotatable coils placed on a common shaft and with magnetic shields; if desired, between adjacent field coils, my invention may be used in -connection with polyphase circuits. In Figure 4 a two unit arrangement is shown which may be used as a two or three phase wattmeter in the well known manner. The fields l1 and H are shown bolted in tandem cooperating with the common shaft l6. 1 To guard against interaction between the field coils, a shield 5| is provided which may be composed of a plate or a stack of laminations composed of relatively permeable magnetic material.

Inaccordance'with the provisions of the patent statutes, I have described the principle of operation of my invention together with the apparatus which I now consider to represent the best embodiment thereof but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carv ried out by other means.

What I claim as new and desire'to secure by Letters Patent of the United States is:

1. A long range wattmeter comprising a laminated field member composed of relatively permeable magnetic material, a field coil, a laminated core and a movable coil, saidfield member being in generally c-shape with an inwardly extending projection added at the mid portion of the 0, said projection having a substantially circular notch therein open at the end of the projection, said field coil surrounding said projection at the neck thereof, said core being in general U-shape with a substantially circular edged yoke portion fitting into the notch in said field projection and spaced from the, edges thereof to form a substantially uniform air gap for the movable coil, said latter coil linking the said circular edged portion of said .core and being'eccentrically mounted to rotate about anaxis extending through the yoke portion of said U-shaped core and substantially concentrlc with the circular edge thereof, said coil having one edge adjacent said axis and the opposite edge in said air gap, said U-shaped core having leg portions extending adjacent the end portion of the C-shaped field member and spaced therefrom to form perceptible air gaps.

2. A long range wattmeter comprising a magnetic flux conducting field structure having an inner pole piece substantially annular in shape surrounded by an outer pole piece and flux paths joining said pole pieces, said pole pieces being spaced to form an annular air gap therebetween, a field coil linking the fiux paths between said pole pieces and a rotatable coil eccentrically mounted with respect to its axis of rotation and with one side thereof passing through said annular inner pole piece and with the other side passing through and adapted to travel in said air gap, the annular pole piece having flux conducting portions attached thereto to form a relatively symmetrical coredivided into two portions with an air gap therebetween, the external magnetic circuit between said pole pieces having an air gap interposed therein of less length than the coilreceiving air gap between the pole pieces, and the air gap between the portions of the core being greater in length than the air gap between the pole pieces.

3. Along range dynamometer instrument comprising a field structure including a pair oi pole pieces with an annular air gap therebetween and portions joining said pole pieces to form a magnetic circuit completed by passage of flux across said air gap, at least one of said pole pieces being substantially annular in shape with a gap therein with branched circuit portions extending from the annular pole piece from either side of the gap therein to the flux conducting portion oi! the field structure, a field coil wound on the other of said polepieces, and a coillinking said annular pole piece with one side passing through it and an axis of rotation passing through said annular pole piece.

4. A long range polyphase dynamometer instrument comprising a plurality of field structures each including a pair of pole pieces with annular air. gaps therebetween, and portions joining said pole pieces to form magnetic circuits completed by passage of flux across said air gaps, a plurality of field coils each carried by one of said field structures and linking it, at least one of each of said pairs of pole pieces being substantially annular in shape with a gap therein, with branched circuit portions extending from the am nular pole piece from either side of the gap therein to the flux conducting portion of the corresponding field structure, said field structures being mounted one in front of the other with said annular pole pieces substantially coaxial, and a plurality of mechanically connected movable coils each linking one of said annular pole pieces with one side passing through the pole piece and having an axis of rotation passing through said annular pole pieces,

5. A long range dynamometer instrument comprising a magnetic flux-conducting field structure including a pair of pole pieces with an annular, air gap therebetween and portions joining said pole pieces to form a magnetic circuit com- V pleted by passage of fiux across said air gap; a field coil linking sa-id field structure, at least one of said pole pieces being substantially annular in shape with a gap'therein with branched clrcui portions extending from the annular pole piece from either side of the gap therein to the flux conducting portion of the field structure, and a coil linking said annular pole piece with an axis of rotation passing through said annular pole piece and a side adapted to sweep through the air gap between pole pieces, the external magnetic circuit in said field structure between said pole pieces having an. air gap interposed therein of less length than the coil-receiving air gap between the pole pieces.

ALMON J. CORSON. 

